German Patent Specification (Offenlegungsschrift) No. 1,510,976 describes a pull-off aid for drawing threads overhead from bobbins of all kinds with the use of an inherently flexible body whose rim is resiliently deformable under the tensile forces exerted by the thread. This disc is generally made from a plastic material and its edge is flexed or bent upwardly by the running thread, whereby the rim of the disc is automatically adapted to the decreasing diameter of the bobbin from which the thread is drawn. This pull-off aid, in the form of a resilient disc, can also be used when the threads are to be guided past the flanks of the bobbins when two or more bobbins are mounted coaxially, one above the other, with the resilient disc disposed between the bobbins. This effectively prevents the thread from the lower bobbin from sliding along the flank of the upper bobbin, preferably in the case of cylindrical bobbins, when, for example, the thread is pulled off overhead.
Thus, the solution in accordance with German Offenlegungsschrift No. 1,510,976 is based on the use of a resilient plastic disc serving as a pull-off aid, such that the plastic disc is deformed in the direction of the take-off of the thread by the tension of the thread resulting from the draw-off forces. The take-up tension of the thread exerts a radial force on the rim of the disc. This radial force causes the disc to flex or bend upwardly until the resilient counter-force of the disc counterbalances this radial force. When two bobbins are mounted one above the other, the disc which is bent up by the draw-off force of the thread from a lower bobbin is applied around the rim of the bobbin located thereabove and thus prevents the thread from the lower bobbin from sliding over the edges of the upper bobbin. Moreover, the tension of the thread from the lower bobbin is affected by the projecting rim of the disc.
However, the known pull-off aids in the form of discs made from resiliently deformable material and having continuous peripheral rims, are still not sufficiently resilient to be able to yield to an adequate extent in the direction in which the thread is drawn off.
German Patent Specification (Offenlegungsschrift) No. 28 27 814 describes a pull-off aid in the form of a disc whose circumferential region comprises a plurality of laminae or segments which are disposed in a fan shape and which partially overlap one another. The elasticity of the rim of the disc is increased as a result of splitting up the outer rim of the disc into a plurality of mutually overlapping laminae or segments, since the thread need only flex or bend upwardly one or two of the mutually overlapping elements more or less only at individual locations. The function of this known pull-off aid has proved to be extremely advantageous in operation, since it can be used to obtain maximum adaptation to varying bobbin diameters, that is to say, decreasing bobbin diameters. However, it may also be seen that, as a result of the required flexibility of the individual laminae or segments, the disc is an element which lacks robustness particularly in the region of its periphery, so that the sensitive rim of the disc can be readily damaged particularly when mounting and handling it, that is to say, when slipping discs of this kind onto a spindle.
German Patent Specification (Offenlegungsschrift) No. 28 27 853 describes a pull-off aid in the form of a substantially rigid annular body which is movable in a radial and lateral direction about the axis of the bobbin. However, it is impossible to adapt the external nominal diameter to, for example, varying bobbin diameters.
An object of the invention is to design a pull-off aid for threads drawn off overhead from at least two coaxial bobbins of the kind described initially, such that it is possible to dispense with flexible and thus sensitive outer rim elements, adaptation to changing, that is to say, decreasing diameters of the feed bobbins, nevertheless being ensured.
A pull-off aid in accordance with the invention comprises at least one disc which can be slipped on to a bobbin carrier and whose periphery is formed by the outer rims of partially mutually overlapping segments which are radially displaceably mounted so that the outer diameter of the disc is adjustable.
It is thus possible to adapt the external diameter of the disc-shaped pull-off aid to varying diameters of the bobbins.
Preferably, the radial displacement of the overlapping segments is controllable in dependence upon the weight of the bobbins or upon the external diameter of the bobbins, or alternatively, in dependence upon time.
In order to render the radial displacement of the overlapping segments, and thus the change in the external diameter of the pull-off aid, independent of the force applied to the pull-off aid by the thread and dependent upon the tension of the thread, the pull-off aid preferably has a resilient element which is effective in the axial direction of the disc and which is loaded by the weight of at least one of the supply bobbins which are mounted one above the other for the purpose of controlling the radial displacement of the segments. In this manner, it is ensured that the external diameter of the pull-off aid is forcibly adapted to changing, that is to say, decreasing diameters of the bobbins, since a reduction in weight goes hand in hand with a reduction in the diameter of the supply bobbins. Thus, in the pull-off aid in accordance with the invention, the external diameter of the pull-off aid is changed in dependence upon the decreasing diameter of the supply bobbins. Thus, when the supply bobbins are full and thus have a large diameter, the pull-off aid has a larger diameter than in the case of bobbins whose diameter has decreased as a result of the drawing-off of thread. Thus, it is ensured that the threads running from the supply bobbins always have a support edge or run-off edge which prevents the threads running off bobbins, from coming into contact with the flank of their own supply bobbin or creel bobbin or the flank of the bobbin located thereabove.
Preferably, resilient elements of different strengths can be interchangeably used for the purpose of adaptation to different bobbin densities or bobbin weights. In accordance with a preferred embodiment of the invention, the inner edges of the segments have an associated cam arrangement which is disposed concentrically of the axis of the disc and which extends conically in an axial direction and against which abuts a support surface arrangement which is adjustable in an axial direction under the influence of the resilient element. Thus, this cam arrangement constitutes a control element in order to deflect the resilient force, effective in an axial direction during reduction of the weight of the bobbin, in a radial direction for the purpose of adjusting the segments.
Preferably, the segments are subjected to the influence of a tensioning element which pulls the segments radially inwardly or which acts upon them.
In order to increase the stability, and in accordance with a further preferred embodiment of the invention, the segments are displaceably mounted between a lower support disc and an upper carrier disc which is held at an axial distance therefrom, and the support disc and the carrier disc can be interconnected by means of spacer pins which at the same time constitute guide elements for the segments displaceable in a radial direction.
Preferably, each segment has at last one lug, such that the lugs of all the segments are distributed substantially uniformly around the axis of the disc, a common resilient tensioning element, preferably in the form of a garter spring or rubber ring, being placed around the lugs.
One preferred embodiment of the pull-off aid in accordance with the invention has a centering sleeve which can be slipped onto the bobbin carrier and which has an outer flange serving as a support element for a supply bobbin core, and an inner annular shoulder serving as an upper stop surface for the resilient element which is disposed within the sleeve. In a development of this kind, the centering sleeve serves as a slip-on sleeve for the lower supply bobbin onto which at least one further supply bobbin is mounted with the disc-shaped pull-off aid in accordance with the invention interposed therebetween, so that the resilient element responds to the combined reduction of weight of the two supply bobbins resulting from the reduction in the diameters thereof.
A modified embodiment of the invention has a support sleeve which can be slipped onto the bobbin carrier and which is mountable on a lower supply bobbin core and which has a lower, radially outwardly projecting annular support serving as a lower support surface for the resilient element whose upper end abuts against an inner annular shoulder of a centering sleeve which is slipped onto the support sleeve and which incorporates an outer flange serving as a support element for a further supply bobbin core. In this modified embodiment of the pull-off aid in accordance with the invention, the resilient means is only stressed by the weight of the upper supply bobbin dependent upon the diameter, so that only the change in the diameter of the upper supply bobbin is also used as a control variable for the change in the diameter of the disc-like pull-off aid.
Alternatively, from the view point of yarn technology, that is to say, the states of tension of the thread running off, intermittent adjustment of the external diameter of the disc is sufficient. Thus, for example, multi-stage adjustments or, if required, a single stage adjustment is possible which occurs when the bobbin has been reduced to approximately half its weight. The change-over point can then lie within predetermined limits which fluctuate approximately between 40% to 60% of the weight of the bobbin relative to the original weight of the fully wound bobbin. This intermittent adjustment can be achieved in that the bottom region of the cam arrangement associated with the inner edges of the segments is of circular cylindrical configuration and its upper region extends conically, so that inwardly directed radial displacement of the segments is only possible when the periphery of the outer flange of the centering sleeve enters the region of the conically extending surfaces of the cam arrangement.
In a further preferred embodiment of the invention, the segments are displaceable radially inwardly to an extent that the lower support disc forms the entire outer periphery of the pull-off aid. The peripheries of the individual segments are of arcuate configuration, so that all the segments accurately overlap one another when they are in their outer radial positions and uniformly form a circular diameter. After the individual segments have been displaced radially inwardly, that is to say, approximately upon reaching half the weight of the bobbins, the outer rims of the segments lie within the external diameter of the lower support disc which has a circular periphery and thus also ensures that the thread will slide along in a trouble-free manner.
In a further development of the invention, a further possibility of continuous or stepwise adjustment of the external diameter of the pull-off aid resides in providing the segments with substantially radially directed feeler fingers which can be brought into abutment against the outer periphery of the bobbins. In an embodiment of this kind, the diameters of the bobbins are sensed, the feeler fingers essentially replacing the cam arrangement described above.